Microwave heating applicator

ABSTRACT

An apparatus for and method of heating or preheating articles with microwave energy. The article is rotatably disposed within an enclosure adapted to be radiated with electromagnetic energy at 915 and/or 2450 MHz by waveguide means terminating in a radiator, such as a flared horn. The end of the radiator is shaped to conform to any article, for example, pneumatic type rubber tires having annular shaped bodies for preheating prior to vulcanization or recapping. Multimode distribution of energy within the enclosure is achieved without resort to mode stirrers. Means are disclosed for altering the displacement of the articles during heating, either vertically or angularly, to provide uniform heating across the article surface.

United States Patent 1 Peterson et al. July 10, 1973 MICROWAVE HEATING APPLICATOR Primary Examiner-J. V. Truhe Hu h D. Jae er 75] Inventors: Robert A. Peterson, Canton, Ass'smm g g Charles L. Gilliatt, Andover, both Attorney Harold Murphy Edgar Rost et Mass 57 ABSTRACT Assigneel Raytheon p y! Lcxington An apparatus for and method of heating or preheating Massarticles with microwave energy. The article is rotatably [22] Filed: 18 1972 disposed within an enclosure adapted to be radiated with electromagnetic energy at 915 and/or 2450 MHz PP 227,547 by waveguide means terminating in a radiator, such as a flared horn. The end of the radiator is shaped to con- 52 US. Cl. 219120.55, 343/786 any W example pmf'umatic W "3 [51] Int. Cl. "05b 9/06 her mes havmg annular Shaped bodles for Preheatmg 58 Field of Search 219/1053 343/786 Prior vulcanizatim mapping- Multimode distribution of energy within the enclosure is achieved with- [56] References Cited out resort to mode stirrers. Means are disclosed for altering the displacement of the articles during heating, 3 127 494 i lfi i PQTENTS 219/10 55 either vertically or angularly, to provide uniform heateoug et th '1 If 3,674,422 7/1972 Gray 219/1055 X mg across e 3 1c 6 Su ace 3,l71,l29 2/1965 Nowakowski 343/786 10 Claims, 7 Drawing Figures Patented July 10, 1973 3,745,291

4 Sheets-Sheet 1 FIG m wt M F 4 Sheets-Sheet 2 NR mNk Patented July 10, 1973 Patented July 10, 1973 4 Sheets-Sheet 5 ILL Patented July 10, 1973 4 Sheets-Sheet A.

1 MICROWAVE HEATING APPLICATOR BACKGROUND OF THE INVENTION The invention relates to heating articles by high frequency energy in the microwave portion of the electromagnetic spectrum and, particularly, articles which are inherently poor thermal conductors, such as, pneumatic type rubber tires.

Vulcanizing and molding, as well as recapping, of pneumatic type rubber articles has been time consuming due to the inherent poor thermal conductivity of the rubber materials. Such articles are generally heated from the outside and in many instances it may take many hours to reach the required working temperatures. It is known that such articles incorporate both natural as well as synthetic rubber along with other ingredients including carbonaceous products. The compounded material, therefore, has an inherent capability for being heated with electromagnetic waves which provide for the generation of heat from within the article. The equilibrium temperature is reached rapidly by reason of the short path of heat conduction. Carbonaceous products, for example, carbon black, are ideal electromagnetic energy absorbing materials which aid in the microwave heating process.

Microwave heating techniques, sometimes referred to as dielectric heating, have previously been utilized in the processing of nonconductive or poor thermally conductive materials including foodstuffs, paper, wood, leather and the like. The means for the generation of such high frequency energy in the microwave portion of the electromagnetic spectrum arose during World War II radar system applications in the form of the magnetron oscillator. A comprehensive description of the construction and operation of such devices is provided in the text Microwave Magnetrons, Radiation Laboratories Series, Vol. 6, by G.B. Collins, McGrawHill Book Company, Inc., 1948. Such energy generators generally operate at allotted Federal Communication Commission frequencies of 915 or 2450 MHz. In the lower frequency band vacuum tube oscillators and klystrons are also employed as energy generators. For the purposes of the present application, the term microwave is defined as electromagnetic energy radiation in that portion of the spectrum having wavelengths in the order of approximately 30 centimeters to l millimeter and frequencies in excess of 300 MHz.

An exemplary embodiment of a prior art apparatus for heating or preheating of rubber articles is disclosed in U.S. Pat. No. 3,566,066 issued Feb. 23, 1971, to J. Borthwick and E. Searle. A chamber of a substantially circular, elliptical or smooth curved cross-sectional configuration is provided with an assymmetrical waveguide feed disposed in the base. Multimode distribution means comprising a motor driven vane-type mode stirrer is disposed adjacent to the waveguide entry means. An axially disposed disc within the chamber carries the article to be heated and is energized by a shaft and motor. Such apparatus provides a heating chamber of completely fixed cross-sectional dimensions to accommodate a particular product which prevents processing of any other shaped articles, particularly larger diameter pneumatic type rubber tires. Energy distribution by means of the base feed together with the mode stirrer provides for relatively inefficient heating of the article particularly in the areas of thicker cross section where the tire treads are formed. This results in longer processing times to achieve the equilibrium temperature for working the article.

SUMMARY OF THE INVENTION In accordance with the present invention a microwave applicator is provided for selectively heating articles, particularly in the regions of thicker cross section. An enclosure, with access means, defined by conductive walls provides for multimode energy distribution when radiated by electromagnetic energy. Means are provided for supporting and rotating the article to be heated within the enclosure. The means for the distribution of the high frequency electromagnetic energy comprise wavequide means terminating in at least one flared horn radiator directed upon the article to be heated. The radiator is fixed in position. The ends of the radiator surrounding the open mouth are shaped to have a contour conforming to that of the article to be heated while being rotated. Means for rotating, as well as vertical displacement, are provided. Angular displacement by tilt axis gearing means also provides for the uniform application of the microwave energy across the surface of the article. The horn radiating means may be disposed diametrically opposite to one another or staggered. In some applications, particularly involving annular articles, the radiating means may be disposed on all four quadrants of a circular path. The enclosure, as well as energy source and radiating means, is adaptable to accept any size article. Hence, tires having diameters of 3 feet up to 15 feet can be easily accommodated in the disclosed apparatus. The energy distribution is achieved by the selective directivity of the energy radiating means thereby eliminating the need for mode stirrers. The adaptability of the apparatus eliminates the need for providing separate units of the type disclosed in the aforereferenced patent for each size tire which would be quite costly. Further, the radiating means provides for a higher heat concentration in the thicker or tread sections and a lower heat in the sidewalls which is particularly advantageous in subsequent vulcanizing operations, such as recapping. The elimination of the mode stirrer also permits the utilization of parallelepiped walls in place of circular, elliptical or smooth curved walls to form the heating enclosure which is advantageous, cost-wise. The selected distribution of the microwave energy by the horm radiator means also minimizes problems of stray energy leakage with conventional mode stirrers distributing such energy throughout a large chamber having numerous entrance and access openings.

BRIEF DESCRIPTION OF THE DRAWINGS Details of illustrative embodiments of the invention will be described with reference directed to the accompanying drawings, wherein: horn FIG. 1 is a plan elevational view illustrating the main components of the embodiment of the invention;

FIG. 2 is a side elevational view with a side enclosure wall removed;

FIG. 3 is a side elevational view of a complete illustrative embodiment of the invention;

FIG. 4 is a plan view of the complete illustrative embodiment with the top wall of the enclosure removed;

FIG. 5 is an isometric view of an illustrative vertical displacement mechanism;

FIG. 6 is an isometric view of an alternative vertical displacement mechanism; and

FIG. 7 is an isometric view of an angular displacement mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, the illustrative embodiment 10 comprises an enclosure 12 defined by parallel conductive walls 14 and 16. An access opening enclosed by door 18 is provided in one of the conductive walls 14 for entrance of servicing personnel while second access means 20 are provided in top wall 22 for the introduction of the article to be heated. Bottom wall 24 provides support means for the article carrier, such as turntable 26, actuated by vertical shaft 28 coupled to rotation and displacement means to be hereinafter described. The shaped annular rubber article 30, such as a pneumatic type tire, is rotatably supported on turntable 26. In FIG. 2 it will be noted that the central section 32 where the vulcanized tread is normally provided is substantially thicker than the adjacent sidewall portions 34.

Electromagnetic energy at a frequency of either 915 or 2450 MHz is distributed within the enclosure by waveguide means 36 suitably connected through walls 16 bycouplers 38 and terminating in a flared openmouthed horn radiator 40. At least one of such energy radiators is utilized with the article being continuously rotated and vertically displaced during heating. The enclosure dimensions are selected to support the distribution of numerous energy modes to provide for uniform heating. In some embodiments the disposition of a diametrically opposed horn radiator 42 from the opposing wall 16 will measurably reduce the heating times. The inner edge of the radiators 40 is shaped to have a contoured end wall 44 adapted to conform to the annular article 30 during rotation. In other desired embodiments it may be advantageous to have energy radiators disposed in all four quadrants surrounding a circular path. One such additional radiator 46 is indicated by the dotted lines in FIG. 1. Additionally, the individual radiators may be staggered to heat at different levels.

Referring now to FIGS. 3 and 4, another exemplary embodiment of the invention will be described. In this embodiment the adaptability of the microwave applicator of the invention to any size product is indicated with a capability of handling articles having diameters as large as feet. The power pack assembly including waveguide means 48 of a rectangular configuration formed by suitable curved and straight sections is coupled by an energy sealing bellows waveguide section 50 to wall 52. The horn radiator 54 is carried on the inside of movable wall 52. The waveguide means are coupled to the electromagnetic energy source 56 including the high voltage power supplies 58 having doors 60 for access to the internal components. Power cables 62 and coolant circulation conduits 64 in the form of flexible water lines are coupled to the power supply. The energy generator which may be a vacuum tube oscillator or magnetron is of conventional form and has not been illustrated.

Wheels 66 provide for the movement of the power pack assembly and wall 52 with a companion assembly disposed on the opposite side. Parallel sidewalls 68 are fixed and an access door '70 provided as shown. The top wall of the overall enclosure is formed by sliding wall sections 72 supported by wheels 74 and are actuated by gear means 76. Two sections are provided and a shelf 78 supports the movable top wall sections 72 in the open position permitting the introduction of the tires which occupy the area indicated by the circle 80. The left-hand portion of FIG. 3 indicates the open position of the sliding wall sections and has been designated 72a. The right-hand portion of this view indicates the closed position of the wall section 72. Normally the sliding wall sections open and close simultaneously and a crane or other such structure is utilized to position the article to be heated within the enclosure. The dotted lines in FIGS. 3 and 4 indicate the movable positions of the illustrative components as well as components underlying movable structures.

For continuous changing of the levels of heat distribution, FIG. 5 illustrates a rotatable and vertical displacement mechanism for carrying the articles being heated. A turntable 32 is mounted on vertical shaft 84 carrying a pulley 86 connected by a belt or chain 88 to a gearbox 90 and motor 92. The entire mechanism is supported on angle iron frames. An elevation mechanism is provided by chains 94 connected to pulleys 96 with the chains maintained at a fixed point by means secured to the walls of the enclosure. The elevation drive comprises gearbox 98 and motor 100 coupled to the vertical chains by a shaft 102 and pulley 104 arrangement. As the rubber article is rotated during the heating operation the horn radiators 54 are maintained at a fixed position while the tire is rotated at speeds of, illustratively, 4 rpm. Any microwave energy not ab- Sorbed by the body of the article is radiated within the metallic enclosure and is eventually absorbed by all parts of the article. In preheating applications, the vertical displacement while the article is rotated provides for heating to temperatures measured at aproximately 200F in the center section 32 while the sidewalls remain at approximately 100F or below. The selective heating of the rubber article will, therefore, enhance the subsequent vulcanization operation to provide a recap or tread in the thicker portions of the article.

Referring now to FIG. 6, an alternative vertical displacement and rotation mechanism is shown. In this arrangement turntable 106 is vertically supported by arbor 108. An elevation and rotation input gearing arrangement 110 actuates gear 112 which meshes with larger driving gear 114 communicating with the turntable 106. A differential gear mechanism 116 is intermediately disposed along with reverse gears 118 controlling gear 120.

An alternative arangement for uniform heating of the article is shown in FIG. 7 which provides for angular displacement during rotation. Turntable 122 supported by arbor 124 is controlled by miter gears 126 and a frame 128. A spline 130 provides for movement of the miter gears with an input gear arrangement 132. The adjustmentof the angular displacement about the vertical axis is controlled by a tilt gearing mechanism 134 attached to frame 128. The rotational movement is controlled by an input gear arrangement 136. The foregoing actuating and displacement mechanisms are only several of the many variations and combinations which will be evident to those skilled in the art. 1

There is thus disclosed a microwave applicator for heating or preheating rubber articles which is adapted to handle numerous product sizes. Uniform heating by efficient distribution of the energy within a conductive enclosure is facilitated by radiating horn means coupled by waveguide means to an electromagnetic energy source. Selective heating with the disclosed apparatus provides for efficient utilization of the microwave heating energy for preheating or heating articles which are inherently poor thermal conductors. Numerous variations, alterations or modifications in the disclosed structure will be evident such as, for example, the vertical staggering of the radiating horn means at various positions surrounding the path of travel of the article being heated. In certain applications such staggering may even be preferable to more costly gearing displacement arrangements. While the articles being heating have been enumerated as being of a rubber composition it is also within the purview of the invention to heat any similar poor thermally conductive materials, for example, those of a thermoplastic composition. It is intended, therefore, that the foregoing description of the invention and illustrative embodiments be considered in the broadest aspects and not in a limiting sense.

We claim: 1. Microwave heating apparatus comprising: an enclosure; a source of electromagnetic energy; means for disposition of an article to be heated within said enclosure; and means for distributing said electromagnetic energy within said enclosure; said distributing means comprising waveguide feed means terminating in an open-ended horn-type energy radiator means with said open end contoured to substantially conform to the shape of said article.

2. The apparatus according to claim 1 wherein said radiator means are disposed on diametrically opposite sides of the article being heated.

3. The apparatus according to claim 1 wherein said radiator means are disposed at staggered levels.

4. The apparatus according to claim 1 wherein said radiator means are disposed in all four quadrants surrounding a circular path of travel of the article within the enclosure.

5. The apparatus according to claim 1 andmeans for rotating said article during heating.

6. The apparatus according to claim 1 and means for vertically displacing said article during heating.

7. The apparatus according to claim 1 and means for angularly displacing said article during heating.

8. The apparatus according to claim 1 wherein said enclosure comprises spaced parallel conductive sidewalls and said radiator means are disposed on at least one of said walls.

9. The apparatus according to claim 8 and means for moving at least one of said walls to alter the spacing therebetween.

10. The apparatus according to claim 1 wherein said enclosure is defined by conductive walls with at least one of said walls having an access opening and a door enclosing said access opening. 

1. Microwave heating apparatus comprising: an enclosure; a source of electromagnetic energy; means for disposition of an article to be heated within said enclosure; and means for distributing said electromagnetic energy within said enclosure; said distributing means comprising waveguide feed means terminating in an open-ended horn-type energy radiator means with said open end contoured to substantially conform to the shape of said article.
 2. The apparatus according to claim 1 wherein said radiator means are disposed on diametrically opposite sides of the article being heated.
 3. The apparatus according to claim 1 wherein said radiator means are disposed at staggered levels.
 4. The apparatus according to claim 1 wherein said radiator means are disposed in all four quadrants surrounding a circular path of travel of the article within the enclosure.
 5. The apparatus according to claim 1 and means for rotating said article during heating.
 6. The apparatus according to claim 1 and means for vertically displacing said article during heating.
 7. The apparatus according to claim 1 and means for angularly displacing said article during heating.
 8. The apparatus according to claim 1 wherein said enclosure comprises spaced parallel conductive sidewalls and said radiator means are disposed on at least one of said walls.
 9. The apparatus according to claim 8 and means for moving at least one of said walls to alter the spacing therebetween.
 10. The apparatus according to claim 1 wherein said enclosure is defined by conductive walls with at least one of said walls having an access opening and a door enclosing said access opening. 